Size dependence of molecular fluorescence enhancement of nanoporous gold

We report molecular fluorescence enhancement of free-standing nanoporous gold with tunable nanopore size. The fluorescence intensity of indocynanine green adsorbed on human-serum-albumin-coated nanoporous gold films significantly increases with decreasing nanopore size. The large fluorescence enhancement results from the near-field enhanced excitation and radiative decay rate of fluorophore due to the strong electromagnetic fields produced by nanosized curvatures as well as the coupling between the neighbor gold ligaments.